PB2380: DEVELOPING GENOMIC TESTS THAT GUIDE LARGE B-CELL LYMPHOMA DIAGNOSIS AND TREATMENT: LYMPH2CX AND LYMPH3CX ASSAYS
Authors: Ryan S. Robetorye, Colleen Ramsower, Catherine Mckinney, Lisa Rimsza
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Although cell-of-origin (COO) determination in diffuse large B-cell lymphoma (DLBCL) and differentiation of primary mediastinal large B-cell lymphoma (PMBL) from DLBCL can be important for guiding subsequent therapy, the interpretation of morphologic and immunophenotypic findings in small, and often crushed mediastinal biopsies can often be difficult. Also, immunohistochemical stains are not able to consistently determine COO in DLBCL and distinguish DLBCL from PMBL compared to gold standard gene expression profiling (GEP)-based assays. Aims: We developed and validated clinical Lymph2Cx and Lymph3Cx GEP assays using formalin-fixed paraffin-embedded (FFPE) tissue specimens in our College of American Pathologists (CAP) and Clinical Laboratory Improvement Amendments (CLIA)-accredited molecular diagnostics laboratory known as the Molecular Diagnostics-Arizona Laboratory (MDAZL). These assays can categorize DLBCL into germinal center B-cell (GCB)-type, activated B-cell (ABC)-type, and unclassifiable (UNC) categories (Lymph2Cx) as well as accurately and robustly differentiate PMBL from DLBCL (Lymph3Cx). Methods: When a hematopathologist identifies a large B-cell lymphoma based on histologic and immunophenotypic assessment of the specimen, Lymph2Cx or Lymph3Cx testing is requested from MDAZL to aid in further classification. Tumor content is assessed using an H&E-stained slide, and then additional unstained slides are used to isolate total RNA from the specimen. The RNA is hybridized overnight on a thermal cycler to fluorescently labelled probes in the assay panels. Probe/RNA complexes are then quantitated and subjected to algorithmic analysis for further classification and subtyping.Results: Over 300 cases have now been tested using the Lymph2Cx or Lymph3Cx assays in our MDAZL laboratory. These assays exhibit a relatively rapid turn-around-time, with average in-laboratory time of 1.8 days and an average of 3.3 days from sample receipt to final report Summary/Conclusion: MDAZL has performed a full clinical validation of the performance characteristics of the Lymph2Cx and Lymph3Cx assays and is the first molecular diagnostics laboratory to offer these GEP-based assays for molecular COO subtyping of DLBCL and distinguishing PMBL from DLBCL. With a relatively rapid turn-around-time, these assays are suitable for use in routine hematopathology practice. Real-world case examples can also clearly illustrate the clinical utility of the assays, especially in cases of small biopsies with prominent crush artifact, cases with non-specific immunohistochemistry, or cases with atypical anatomic site presentations, such as mediastinal DLBCL or non-mediastinal PMBL. It is likely that with the development of more personalized approaches to lymphoma therapy in the near future, these assays will become part of the standard of care for aggressive B-cell lymphomas along with existing immunohistochemistry, flow cytometry, fluorescence in situ hybridization, and gene mutation analyses. Keywords: Gene expression profile, B cell lymphoma, Prognosis, Diagnosis